It is known in the art to provide a method of displacing some of the headspace gases in a filled beverage container with gaseous nitrogen. Headspace gas typically contains air, being approximately 78% Nitrogen and 21% Oxygen. The common method of ‘inerting’ a headspace is desirable to provide a reduction in oxygen within a headspace in order to prevent oxidation of sensitive beverages. The displacement of Oxygen by an inert Nitrogen or Carbon Dioxide environment reduces the oxidation of the product that would rapidly occur after sealing therefore, from contact between the headspace O2 and the liquid product.
The methods of displacing headspace gas with gaseous introduction of Nitrogen do not cause a rise in pressure in the headspace, however, as the container is not sealed and the incoming gas simply replaces the existing headspace gas—with the existing gas being ejected or displaced from the container with a resulting maintenance of ambient pressure values.
Once a liquid has been filled into a beverage to a fill-point, the headspace gas above the liquid will have a first pressure prior to sealing with a cap—ambient fill pressure.
It is impossible to introduce a gas (in its natural ‘gaseous’ form) into an unsealed headspace and cause an appreciable rise in pressure that can then be sealed within the container unless the gas is first introduced in a liquefied form and allowed to subsequently transform to its gaseous form.
For this reason, the only known method for causing a rise in headspace pressure through introduction of a gas has been through the introduction of liquid Nitrogen—whereby the liquid Nitrogen is still rapidly expanding as the cap is placed on the container. Soon after the cap is applied there is a build-up of pressure as the boiling Nitrogen expands but is unable to escape the sealed container. See Zenger U.S. Pat. Nos. 5,033,254 and 5,251,424 both of which are incorporated by reference in their entirety.
Most production facilities are searching for ways to reduce costs as a small savings on the cost of each single container, for a food or beverage packer, this quickly adds up to tremendous savings, based on the large number of containers processed. Utilizing lighter weight containers or reducing utility costs are good savings methods.
However, lighter weight containers for noncarbonated products can collapse when stacked unless special handling requirements are satisfied.
For this reason one typical method used to increase stacked weight capability, or top-load strength, in cold fill containers is to dose the container with liquid nitrogen prior to capping. When dosed into a container, liquid nitrogen will provide some internal pressure, which allows the containers to be stacked several pallets high.
As the nitrogen disperses immediately upon injection, however, the process for controlling accurate dosing is limited. Some of the nitrogen will escape prior to capping, thus rendering the process inexact in terms of pressure control. Additionally, handling nitrogen systems can be costly and dangerous.
Following capping there is a subsequent rise in internal pressure as the nitrogen continues to expand but cannot escape the sealed container. However, as the nitrogen is dosed prior to sealing there is loss of some of the nitrogen dose prior to sealing. This varies according to many factors, including variations in product temperature, small variations in actual bottle size resulting in larger or smaller headspace volumes, and fill point variations in the container further affecting the size of headspace volumes between containers This leaves the process inexact in terms of identifying the dose actually in the container after sealing, as the ‘shot’ of liquid Nitrogen is held at a constant volume whereas the shot required is varying. It is accepted that this will always be a value less than the dose introduced to the open container prior to sealing.
The use of nitrogen, however, does provide for a build-up of internal pressure within a container following capping. This is more practical in the case of beverages filled into the container cold, than when used in conjunction with hot fill beverages. In both cases it is possible that all dosed nitrogen disperses prior to sealing the container, for example if there is a stoppage on the line post dosing and prior to capping. However, in a cold filled application the result would be a container that at least is capped at ambient pressure and will remain at ambient pressure. While the benefit of increased top load and sidewall strength would be lost, the result is not particularly damaging as the container would still look attractive to the consumer when purchased.
Plastic bottles need to be pressurized at all line speeds, and if control over the exact pressure achieved inside a container is compromised then the speed of the system will also be compromised in order to correctly pressurize each container.
In the case of a hot filled beverage, an insufficient dose results in the container being sealed at ambient pressure and possessing little ability to pressurize the container following sealing. As the liquid contents of the container subsequently cool, and contract, a vacuum will build and the container will distort as a result. This is not attractive for the consumer.
Additionally, the dosing process becomes even more difficult to control in the hot fill environment, particularly at fast line speeds. When liquid nitrogen is introduced into a container under ambient pressure conditions and on top of a heated liquid, the nitrogen will be much more volatile than if the liquid was cold. It will disperse much more quickly prior to capping or sealing leaving the consistency of dose even more uncertain. A stoppage in the line is therefore more damaging to consistency of dose. For this reason, containers are often overdosed as a precautionary measure, and this is still not ideal.
A typical 18 fl oz (600 ml) polyethylene terephthalate (PET) bottle with a 1 fl oz (30 ml) headspace and pressure specification of 17 psig will need approximately 0.001411 oz (0.04 g) of liquid nitrogen. The dose of liquid nitrogen will boil away and expand to 1.163 fl oz (34.4 ml) of room temperature nitrogen gas after the container is sealed. Add 1.163 fl oz of gas to a sealed volume of 1 fl oz, and you end up with 17 psig.
The challenge for the liquid nitrogen dosing equipment manufacturer is to control the boiling liquid and deliver the 0.001411 oz consistently at speeds from 40 bottles/min to more than 1,000 bottles/min. The dosing equipment can control the liquid nitrogen up to the dosing point, but as already now disclosed it cannot control the liquid nitrogen's behavior once it has been dosed into the container. The liquid nitrogen will boil away rapidly as the container travels to the capper or seamer. An attempt to minimize this problem by placing the <loser as close as possible to the capper prior to sealing is disclosed in U.S. Pat. No. 7,219,480 to Winters et al, which is also incorporated herein by reference in its entirety
Another aspect to consider is consistent container fill levels. Conventionally, the dosage of liquified gas dispensed into a container is based on an average expected fill level of the containers in a continuous fill operation. Using this method, any variation in head-space volume due to variations in fill level would cause under and over pressurized containers. For example, suppose the bottle previously mentioned had an 18 fl oz fill with a 1 fl oz headspace, and the next bottle on the production line had a fill of 18.3 fl oz (610 ml) with a 0.6 fl oz (20 ml) headspace. Both bottles receive a 0.001411 oz charge of liquid nitrogen. The liquid nitrogen dosing is consistent; however, in accordance with basic gas laws, the final bottle pressure on the 18 fl oz fill is 17 psig and the bottle with a 18.3 fl oz fill has 25.5 psig final pressure.
Problems of uniform pressurization remain as a major problem with liquid nitrogen dosing, especially when used with hot-fill beverages.
So called ‘hot fill’ containers are well known in prior art, whereby manufacturers supply PET containers for various liquids which are filled into the containers and the liquid product is at an elevated temperature, typically at or around 85 degrees C. (185 degrees F.).
The container is manufactured to withstand the thermal shock of holding a heated liquid, resulting in a ‘heat-set plastic container. This thermal shock is a result of either introducing the liquid hot at filling, or heating the liquid after it is introduced into the container. In typical prior art filling situations, containers are filled with a heated liquid above 70 degrees C., and more often subjected to filling temperatures of between 70 degrees C. and 95 degrees C. Once capped, or in other words sealed, the product must be maintained at a certain high temperature for a certain critical time in order to complete the process of pasteurization within the container. Even further, the container must also be inverted or at least tipped sideways for a certain time in order to sterilize the underneath of the seal or cap.
It is preferable for example to maintain a temperature of above 80 degrees C. for a 2 minute period after sealing for many beverages prior to starting the cooling process. Therefore the typical cooling of containers to bring them down to around 30 degrees C. does not start until at least some time after the inversion of the container so that the core temperature of the liquid within the container is maintained high enough to sterilize the underneath of the cap and complete sterilization of the internal container contents.
Once the cooling process is finally allowed to be deployed on the container it is usually cooled rapidly in a heat exchanger or cooler in order to provide a container that may be subsequently labelled and packed into boxes or the like for transportation away from the filling line.
Therefore, in prior art it is not considered feasible to provide cooling simultaneously with the capping of filled containers, or the temperature of the contents is compromised before it may be utilized for internal sterilization purposes. Not only would there be substantial risk in introducing foreign matter into the container prior to sealing, but the temperature of the product would be compromised and the efficacy of the pasteurization model would be corrupted.
Once the liquid cools down in a capped container, however, the volume of the liquid in the container reduces, creating a vacuum within the container. This liquid shrinkage results in vacuum pressures that pull inwardly on the side and end walls of the container. This in turn leads to deformation in the walls of plastic bottles if they are not constructed rigidly enough to resist such force.
Typically, vacuum pressures have been accommodated by the use of vacuum panels, which distort inwardly under vacuum pressure. Prior art reveals many vertically oriented vacuum panels that allow containers to withstand the rigors of a hot fill procedure. Such vertically oriented vacuum panels generally lie parallel to the longitudinal axis of a container and flex inwardly under vacuum pressure toward this longitudinal axis.
In addition to the vertically oriented vacuum panels, many prior art containers also have flexible base regions to provide additional vacuum compensation. Many prior art containers designed for hot-filling have various modifications to their end-walls, or base regions to allow for as much inward flexure as possible to accommodate at least some of the vacuum pressure generated within the container.
Even with such substantial displacement of vacuum panels, however, the container requires further strengthening to prevent distortion under the vacuum force.
The liquid shrinkage derived from liquid cooling, causes a build-up of vacuum pressure. Vacuum panels deflect toward this negative pressure, to a degree lessening the vacuum force, by effectively creating a smaller container to better accommodate the smaller volume of contents. However, this smaller shape is held in place by the generating vacuum force. The more difficult the structure is to deflect inwardly, the more vacuum force will be generated. In prior art proposals, a substantial amount of vacuum may still be present in the container and this tends to distort the overall shape unless a large, annular strengthening ring is provided in horizontal, or transverse, orientation typically at least a ⅓ of the distance from an end to the container.
The present invention relates to both cold and hot-fill containers and may be used by way of example in conjunction with the hot fill containers described in international applications published under numbers WO 02/18213 and WO 2004/028910 (PCT specifications) which specifications are also incorporated herein in their entirety where appropriate.
The PCT specifications background the design of hot-fill containers and the problems with such designs that were to be overcome or at least ameliorated and in particular the use of pressure compensation elements.
A problem exists when locating such transversely oriented panels in the container side-wall, or end-wall or base region, even after vacuum is removed completely from the container when the liquid cools down and the panel is inverted. The container exits the filling line just above a typical ambient temperature, and the panel is inverted to achieve an ambient pressure within the container, as opposed to negative pressure as found in prior art. The container is labelled and often refrigerated at point of sale.
This refrigeration provides further product contraction and in containers with very little sidewall structure, so-called ‘glass look-a-like’ bottles, there may therefore be some paneling that occurs on the containers that is unsightly. To overcome this, an attempt is made to provide the base transverse panel with more extraction potential than is required, so that it may be forced into inversion against the force of the small headspace present during filling.
This creates a small positive pressure at fill time, and this positive pressure provides some relief to the situation. As further cool down occurs, for example during refrigeration, the positive pressure may drop and may provide for an ambient pressure at refrigerated temperatures, and so avoid paneling in the container.
This situation is very hard to engineer successfully, however, as it depends on utilising a larger headspace in order to compress at base inversion time, and it is less desirable to introduce a larger headspace to the container than is necessary in order to retain product quality.
While it is desirable to have the liquid level in the container drop, to avoid spill when opened by the consumer, it has been found that providing too much positive pressure potential within the base may cause some product spill when the container is opened, particularly if at ambient temperatures.
In most filling operations, containers are generally filled to a level just below the containers highest level, at the top of the neck finish.
Maintaining as small a container headspace as possible is desirable in order to provide a tolerance for subtle differences in product density or container capacity, to minimize waste from spillage and overflow of liquids on a high-speed package filling line, and to reduce container contraction from cooling contents after hot fill.
Headspace contains gases that in time can damage some products or place extra demands on container structural integrity. Examples include products sensitive to oxygen and products filled and sealed at elevated temperatures. A problem in prior art is the amount of Oxygen present in the headspace gas, typically as a 21% percentage of air.
Filling and sealing a rigid container at elevated temperatures can create significant vacuum forces when excessive headspace gas is also present.
Accordingly, less headspace gas is desirable with containers filled at elevated temperatures, to reduce vacuum forces acting on the container that could compromise structural integrity, induce container stresses, or significantly distort container shape. This is also true during pasteurization and retort processes, which involve filling the container first, sealing, and then subjecting the package to elevated temperatures for a sustained period.
Those skilled in the art are aware of several container manufacturing heat-set processes for improving package heat-resistant performance. In the case of the polyester, polyethylene terephthalate, for example, the heat-setting process generally involves relieving stresses created in the container during its manufacture and to improve crystalline structure.
In hot filling of beverages in PET containers, the thermal stability of the material of the container also constitutes a challenge. PET has a low glass transition point of approximately 75 degrees C. When the headspace of a container is pressurized while the liquid contents are above about 70 degrees C., the container walls are subjected to particularly damaging forces. This occurs following the capping of a lightweight container filled with a heated liquid, even when additional pressure is not applied to the container. The build-up of pressure comes from the headspace increasing in temperature immediately following capping and exerting expansion forces against the lightweight surfaces of the container.
In the current art for both cold and hot filled beverage applications, the containers may be conveyed through a nitrogen-dosing unit where nitrogen may be dripped into the unsealed bottles and shortly afterwards the bottles are sealed. This method is also referred to as the nitro-dose process. Liquefied gas may be injected by an apparatus such as that disclosed in US Patent Application No. 2005/011580 A1 to Siegler et al., which is incorporated herein by reference in its entirety.
Typically, a polyethylene terephthalate container intended for a cold-fill carbonated beverage has higher internal stresses and less crystalline molecular structure than a container intended for a hot-fill, pasteurized, or retort product application. However, even with containers such as described in the abovementioned PCT specifications where there is little residual vacuum pressure, the neck finish of the container is still required to be very thick in order to withstand the temperature of fill.
In nitro-dose applications there is significant container distortion when the PET material is above about 70 degrees C. to 75 degrees C. due to the high level of nitrogen pressure within the container. Such distortion is non-recoverable. The container effectively grows in volume and the base is disfigured and unstable.
Also for example, structures in the sidewall, such as ribbing, may be similarly affected causing uncontrolled container growth and distortion. This distortion causes a weakness in any strengthening structures and is very undesirable.
Typically, at present, hot closed bottles will be transported to the bottle cooler preferably by means of at least one conveyor belt. In the cooling device or heat exchanger, the hot bottle is cooled down close to room temperature or to around 30 degrees C. to 35 degrees C.
Typical hot fill operations utilize ambient water to slowly cool hot filled packages after they are sealed, until they return to ambient temperature. This usually occurs several minutes after the product has been filled into the container, whereby the container walls are subjected to temperatures above the glass transition point of PET.
The temperature of the filled contents take a period of time to cool from a typical 85-95 degrees C. of fill temperature to below approximately 60 degrees C. At 60 degrees C. and below the PET does not distort under stress of internal pressure in the way it does above its glass transition point.
My PCT patent specification WO 2005/085082 describes a previous proposal for a headspace displacement method which is incorporated herein in its entirety where appropriate by way of reference.
Where reference in this specification is made to any prior art, this is not an acknowledgment that it forms part of the common general knowledge in any country or region.